Blast

Some attacks affect everything within an area, their damage
tapering off over distance. This effect is called blast.

Damage that tapers off is often referred to as blast damage.
Blast damage is not a unique damage type, but rather refers
to these rules. Many types of damage are automatically blast
damage.

Every blast attack has a base area of effect — a blast increment
— that’s measured in squares, and a center area called Ground Zero. With a blast radius of 1 square, Ground Zero is the square
in which the blast attack lands or from which it is emitted (e.g. the
square in which a grenade lands). With a larger blast increment,
Ground Zero must contain the origin square, but may be shifted
per the character’s discretion (with a hit) or the GC’s discretion
(with a miss).

Each character, object, and scenery item within Ground Zero
squares suffers the blast’s full damage or numerical effect. This
damage or effect is reduced to 1/2 (rounded down) within each
blast increment out from Ground Zero, until the damage drops
below 1 point, at which point it has no effect.

Blast never turns or bends, and only proceeds through cover
when the cover fails its Damage save.

A blast attack may take the shape of a circle or a 90-degree
cone. For a graphic illustration of each, consult the Blast diagrams.

When a blast attack’s damage or effect is entirely contained within a space smaller than its outermost blast increment covers (e.g. an explosion rips through the interior of a pressurized plane too small to hold 1 or more blast increments), the damage or numerical effect within the contained area increases by 2d6 per interrupted or prevented increment. This does not happen if the blast damage pierces the space’s containment (e.g. breaks a hole through the aforementioned plane’s hull). For a graphic illustration of a contained blast attack, consult the Interrupted Blast Diagram.

Likewise, when a blast attack’s damage or effect is completely
covered by a character’s body (e.g. he leaps onto a live grenade),
the damage decreases by an amount equal to the character’s
Constitution score before it spreads. In this case, the character
covering the effect suffers the maximum possible damage (i.e. as
if the highest possible number were rolled on each damage die).

Blast damage expands vertically and horizontally at the same rate.

Special Note: Unless otherwise specified, any blast attack has
an increment of 1 square and expands as a radius.